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Interferometric Complex Filter

IP.com Disclosure Number: IPCOM000080601D
Original Publication Date: 1974-Jan-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 3 page(s) / 59K

Publishing Venue

IBM

Related People

Lin, BJ: AUTHOR [+2]

Abstract

Described is a structure which uses three intensity plates as a complex filter for an optical input beam. Instead of using a sandwiched complex filter that requires a phase plate, the input beam can be splitted, so that each goes through an intensity filter to be recombined into the output beam. This way, the output beam is still modified in intensity and phase, but the problem of making a phase plate to specification is avoided.

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Interferometric Complex Filter

Described is a structure which uses three intensity plates as a complex filter for an optical input beam. Instead of using a sandwiched complex filter that requires a phase plate, the input beam can be splitted, so that each goes through an intensity filter to be recombined into the output beam. This way, the output beam is still modified in intensity and phase, but the problem of making a phase plate to specification is avoided.

Mathematically, the operation is simply the superposing of base vectors in the complex space to form an arbitrary complex vector. Since negative value is not allowed on the intensity plates, only positive base vectors can be used. The least number of positive base vectors that span the whole complex space is three. The symmetrical ones are, 1, 120 degrees, and 240 degrees. They indicate optical path length differences of zero, one-third-wave and two-third- wave in the splitted three beams, respectively.

Comparing the present technique with a previously known four beam method, a significant resulting improvement is higher optical efficiency. The inherent energy loss due to the absorption of the intensity plates is now two-thirds, instead of three-fourths of the input energy. Other advantages are simpler instrumentation, easier adjustments, and less plates to be made. A combination of ordinary semitransparent beam splitters may be used for the beam splitting and recombining purpose, or the zeroth and the two...